Mechanical impact printers are known to the prior art for imprinting a succession of characters, which may be expressed in the form of a bar code or the like, on an elongated strip of print stock. In such printers, the elongated strip of print stock is caused to substantially continuously move along a predetermined path by being drawn from a spool thereof mounted on a rotatable, print stock supply reel, guided to a print station where the characters are successively printed, and guided to and passed between a rotating, print stock drive capstan and associated pinch roller. An elongated strip of ribbon stock is also caused to substantially continuously move along a predetermined path by being drawn from a spool thereof mounted on a rotatable, ribbon stock supply reel, guided to the print station, and guided to and passed between a rotating, ribbon stock drive capstan and associated pinch roller.
In order to insure proper operation for the impact printer, both the print stock and the ribbon stock must be maintained under substantially constant tension as they are moved along their respective predetermined paths to and from the print station. If the stock tension is too high, then the stock is likely to break or tear. Conversely, if the stock tension is too low, then the stock may shift during imprinting, resulting in a lack of accuracy and precision in the imprinted characters.
The prior art, as typified by U.S. Pat. No. 3,866,851, Brooks, issued on Feb. 18, 1975 to the assignee of the present invention, teaches apparatus for regulating the tension in an elongated strip of print or ribbon stock. Such prior art apparatus includes a lever arm which is supported for rotation about an axis proximate to a rotatable spindle supporting the stock supply reel. A roller is provided on an end of the lever arm away from its axis of rotation, with the elongated strip of stock passing around the roller after being drawn from a spool thereof mounted on the stock supply reel. A spring biases the lever arm to a predetermined angular position, and a braking means is responsive to rotation of the lever arm from its predetermined angular position for varying a braking force applied to the spindle. The braking force is at a maximum when the lever arm is in its predetermined angular position, and decreases as the lever arm is rotated away from that predetermined angular position.
In operation, movement of the elongated strip of stock along its predetermined path causes the lever arm to rotate toward the direction of stock movement and against the force of its associated spring. As the lever arm continues to rotate, the braking force exerted on the spindle is progressively reduced so that the stock supply reel rotates relative to the lever arm to permit the elongated strip of stock to be drawn out. Those skilled in the art will appreciate that the tension in the elongated strip will first increase and then progressively decrease as the stock supply reel rotates relative to the lever arm. Rotation of the lever arm toward the direction of stock movement continues until an equilibrium position, representing the desired stock tension, is reached at which the force exerted on the elongated strip by the spring of the lever arm is balanced by the braking force exerted on the spindle. Thereafter, the prior art tensioning apparatus will attempt to maintain the stock tension at the desired value thereof, e.g., a decrease in stock tension will cause the lever arm to rotate back toward its predetermined angular position to increase the braking force applied to the spindle so as to increase the stock tension.
The tensioning apparatus of the prior art, although providing acceptable operation in most applications, includes an assembly of quite a number of springs, arms, cams, and brake arms, as can be seen from a review of the aforementioned U.S. Pat. No. 3,866,851. Such an assembly is not very compact and cannot be used in certain applications in which space is at a premium. Because of the number of components involved, the assembly is also relatively expensive to manufacture, install and adjust.
It is therefore an object of this invention to provide an improved apparatus for regulating the tension in a tape such as an elongated strip of print or ribbon stock used in printing apparatus.
It is a further object of this invention to provide such a tensioning apparatus which can be constructed as an assembly from a minimum number of components and which accordingly is inexpensive to manufacture and to install.
It is yet a further object of this invention to provide such a tensioning apparatus which is relatively easy to adjust for proper operation, once installed, and which does not require readjustment during continued operation thereof.
It is another object of this invention to provide such a tensioning apparatus which, in addition to regulating the tension in the tape at a substantially constant value, also includes components for positively and repeatably indicating abnormally high and abnormally low values of tape tension.
It is yet a further object of this invention to provide a tensioning apparatus which is compact and which accordingly can be used in applications in which space is at a premium.